I’ve been teaching the benefits of shooting RAW (instead of JPG) for more than a decade. About a year ago, while developing the new display engine for Technical Camera and Kuuvik Capture 4, I did discover another strong reason why you should stop shooting JPG if you care about image quality.
Let me review the usual arguments first.
Limited, 8-bit depth. Digital cameras record at 12 to 16 bits per pixel. Even old ones and your iPhone are 12 bit devices, high-end digital backs are 16. Contemporary DSLR and mirrorless offerings record at 14 bits per pixel. Converting these high bit depth images back to 8 will have serious impact on dynamic range and color range. This is because the 256 possible steps in a JPG aren’t enough to describe a huge range of light and color. And then banding rears up its ugly head. For example, colorwise you are limited to the Adobe RGB color space, while your camera is capable of recording much more.
Fixed white balance. Once a JPG is created, white balance is fixed for good, and cannot be modified later on. You can tweak a little with hard Photoshop work, but it’s quite disastrous.
Lossy compression. The JPG format was designed to compress the hell out of image data. Consequently, you lose some data even on the highest compression quality setting. And digital cameras tend not to use the highest compression quality.
And here’s the last argument:
4:2:2 or 4:2:0 chroma subsampling. If you aren’t familiar with chroma subsampling, read the Wikipedia article first. All Canon and Nikon cameras I’ve seen files from use 4:2:2 subsampling, which means that the color information is halved horizontally. iPhone JPGs are even worse with 4:2:0 subsampling, that is, 3/4 of the color information is missing (you won’t notice it, because the heavy-handed over-processing in these files make them look like crap at actual pixels level anyway). As a comparison, the JPG Quarter HQ image quality setting in Technical Camera uses 4:4:4 chroma subsampling that preserves full color information at every pixel. These HQ files also use higher compression quality setting and are usually quite large.
As you see, JPG files are handicapped at every imaginable level. That’s fine for web display, but make this format totally unsuitable for image capture. Storage is dirt cheap these days, for example a high quality 32GB SanDisk Extreme Pro SD card sells for less than $15, and can store a thousand 26 megapixel images in my EOS RP. In my opinion even lossy RAW compression (such as C-RAW in new Canons) has zero significance in terms of storage. Go with the highest quality, lossless RAW. There will come a time when you’ll be grateful that you did.
